1. Field of the Invention
The present invention relates to personal computers and more particularly to a liquid crystal display device for use in a laptop type personal computer which is so compact and lightweight that it can be carried on lap and which has performance comparable to that of disctop type computers, a word processor or a notebook type personal computer.
2. Prior Art
In the past, a liquid crystal display device having the following construction has been known as this type of liquid crystal display device.
(1) As will be described with reference to FIGS. 1 to 3, the known device comprises a liquid crystal device panel 1 and a lighting unit 12 for backlighting of the liquid crystal device panel 1.
The lighting unit 12 includes a transparent optical conductor 4 disposed in parallel with the liquid crystal device panel 1 rearwardly thereof, an opaque support 6 for supporting the transparent optical conductor 4 at a predetermined position relative to the liquid crystal device panel 1, a tubular light source 8 disposed near one end of the transparent optical conductor 4, and an opaque reflector 7 disposed laterally of the tubular light source 8 and adapted to reflect light, emitted from the tubular light source 8, toward the transparent optical conductor 4. A light diffusion sheet 3 is interposed between liquid crystal device panel 1 and transparent optical conductor 4 in order that light reflected from a reflector sheet 5 interposed between the opaque support 6 and transparent optical conductor 4 and light from the transparent optical conductor 4 can be diffused to illuminate the entire back surface of the liquid crystal device panel 1.
The liquid crystal device panel 1 is held, at its upper peripheral edge and sides, by a box-like outer frame 2. One end of the outer frame, remote from the tubular light source 8, terminates in a -letter shaped (in sectional form) recess in which a Z-shaped end of the opaque support 6 is inserted, and a liquid crystal control drive element 10 is surrounded by the liquid crystal device panel 1, Z-shaped end and -letter shaped recess.
A silicon cushion 9 is interposed between the light diffusion sheet 3 and one end of the liquid crystal device panel 1 so that even when impact hits the outer frame 2, the cushion 9 may absorb the impact to prevent the sheet 3 and panel 1 from being damaged (see FIG. 3).
(2) Another liquid crystal display device is also known having construction as shown in FIG. 4 wherein a transparent optical conductor 4 and a member corresponding to the aforementioned opaque support 6 are made of the same transparent material and formed integrally with each other or as a unitary structure, the support 6 has one reversed L-shaped end opposite to the other end at which a tubular light source is placed (see FIG. 2), which reversed L-shaped end is inserted in a -letter shaped recess of an outer frame 2, and a reflector sheet is provided on the bottom of the transparent optical conductor 4.
The reason why the outer frame 2 and opaque support 6 are formed as separate members in the conventional liquid crystal display device shown in FIGS. 1 to 3 is that when the liquid crystal device panel 1 and transparent optical conductor 4 conveyed from separate production lines are to be fixed back to back, it is more convenient from the standpoint of production process to separately produce the outer frame 2 for holding the liquid crystal device panel frontally thereof and the opaque support 6 for supporting the liquid crystal device panel rearwardly thereof and put them together upon assembling than to support the liquid crystal device panel and transparent optical conductor by using a single support member.
Further, the aforementioned transparent optical conductor 4, opaque support 6 and a combination light source cover and reflector 7 are members of different materials which are produced separately.
Further, in the conventional liquid crystal display device, the opaque support 6 and the combination light source cover and reflector 7 are separate members as best seen in FIG. 2 and in order to secure strength of each of the opaque support 6 and light source cover and reflector 7, both made of resin, their thicknesses must be increased. Under the circumstances, in the device shown in FIGS. 1 to 3 wherein the box-shaped opaque support 6 supports the back of the transparent optical conductor 4 to form a double layer structure of the transparent optical conductor 4 and opaque support 6, the device is increased in thickness in proportion to an increase in thickness of the opaque support 6 and cannot meet requirement of thickness reduction. Conceivably, with a view of reducing the thickness of the opaque support 6, the opaque support 6 may be made of extensible hard metal material but in this case a sheet metal treatment procedure is needed, complicating the working and besides the liquid crystal display device is increased in weight. In addition, reflecting power of an opaque support made of metal is smaller than that of the conventional opaque support of plastic material and optical loss at the end of the transparent optical conductor 4 increases. Even if metal paint treatment for reflection is applied at the cost of an additional painting process, the resulting reflecting power is still smaller than that of the resin material. Accordingly, the advent of a liquid crystal display device has been desired which uses an opaque support 6 made of a plastic material as in the conventional device and which can be reduced in thickness.
Further, as will be seen in FIG. 3, in the conventional liquid crystal display device, there is a gap 4a between one end of transparent optical conductor 4, where no tubular light source 8 is arranged, and the opaque support 6 and accordingly light within the transparent optical conductor 4 leaks to the gap 4a, causing an optical loss.
In the conventional liquid crystal display device shown in FIG. 4, the transparent optical conductor 4 and the (opaque) support 6 are made of the same material and formed integrally with each other to provide a support structure and hence light within a transparent optical conductor region of the support structure propagates also to a region of the support 6 which is clear of an effective display area L of liquid crystal device panel 1, with the result that light emitted from the tubular light source (see FIG. 2) cannot efficiently propagate and diffuse into the liquid crystal device panel 1, thus preventing high brightness capability.